1. Field of the Invention
This invention pertains to boat trailers, and more particularly to apparatus that facilitates launching and loading boats onto trailers.
2. Description of the Prior Art
Numerous kinds of trailers have been developed to load, transport, and launch boats. In general, boat trailers can be classified into two basic types: trailers having only rollers arranged to support the boat hull on the trailer frame, and trailers having two or more bunks that support the boat hull. Bunk trailers often include at least one roller, usually at the tongue end, to protect a portion of the boat hull while loading. Examples of roller trailers may be seen in U.S. Pat. Nos. 3,785,677; and 4,329,108. U.S. Pat. Nos. 3,917,087 and 4,464,092 show combination bunk-roller trailers.
Roller trailers possess the advantage of reducing the friction force that must be exerted in launching and loading a boat. On the other hand, roller trailers have several disadvantages. To adequately support a hull, a large number of rollers are required. The rollers must be adjustable to suit different boat hull configurations, and the adjustments must be made with care so that all the rollers share in supporting the hull. Even when all the rollers are in contact with the hull, the total support area provided by the rollers is relatively small. As a consequence, the rollers have a tendency to flatten, which eliminates the initial advantage of low-friction operation. Rollers also tend to dimple hulls, and some boat manufacturers do not warrant their boats if they are transported on roller trailers. In addition, to be effective, the rollers must be pivotable in one or more directions relative to the trailer frame. The large number of rollers, together with the various components needed to pivot and adjust them, results in objectionable expense. Further, the brackets for pivoting the rollers occupy space in a manner that places the rollers at a relatively great distance above the trailer frame. The result is that the center of gravity of a loaded boat is undesirably high above the ground. Another common problem associated with roller trailers is that boats easily become misaligned on the rollers as the boats are loaded from the water. Yaw misalignment is especially common and troublesome. As a result, boaters frequently must push their partially loaded boats back into the water and make additional attempts to load them in proper alignment with the rollers.
Bunk trailers have the advantages of low cost relative to roller trailers and of providing a large support area for the boat hulls. On the other hand, bunks produce large friction forces that must be overcome to launch or load a boat. In addition, bunks usually are made of wood covered with a carpet-like material, which deteriorate relatively quickly in marine use.
Thus, a need exists for a trailer having improved means for supporting boat hulls.